Underwater GPS

[DoUDive2]

World wide, the 95% accuracy of GPS is 8 to 15 meters (25 to 50 ft).

 

[DoUDive2]

There is a system known as the Cobra-Tac on the market now that is able to track divers location by entering the water at a known point (GPS coordinate). The unit tracks the divers depth and movements to calculate the current position, this technology is not classified but is pretty costly... (going from memory, between $15,000 and $20,000)

It is also primarily an inertiial system, meaning that its positioning accuracy degrades with time. The concept of using a pressure sensor to determine the altitude (depth) of the diver is an innovative idea that allows the unit to significantly reduce the rate at which the position accuracy degrades. However, even with the pressure sensor, the accuracy of the system is degrading at 0.5 cm/s*. That means that after an hour of being underwater the Cobra-Tac position error will typically be about:

0.005 m/s * 3600 s = 18 m (or 60 ft)
Chris

*reference: RJE Cobra-Tac Data Sheet

 

[alemaozinho]

what about a navigation specialty course mmmhh?

 

[tfohl]

Another approach is to use an acoustic positioning system. See, for example, http://www.plsm-instrumentation.com/site_an/. They require that you create a bench mark at a known position (with a surface GPS for example) and your underwater position is determined quite accurately by acoustic signals. The range depends on signal strength but the accuracy is always there--for a price.

Best,
Tim Fohl

 

[Joffren]

don't submarines use gps? of course their technology may not quite be in our price range.

Actually, submaries use a gyroscopic device that works essesntially like an "underwater GPS". Because the underwater environment is "3D", a gps which works by cross referencing or triangulating the position of the gps receiver this would not be practical underwater even if the signals would reach.

 

[Joffren]

Thank the government for the inaccuracy of GPS. The gov't uses Selective Availabilty, which is a program that makes
GPS innacurate by a varying degree, but no more than 350 feet. Nowadays, though, most GPS are WAAS enabled. WAAS is a feature that cross references radio signals from permanent land-based locations therefore making the reading accurate to .49" Yes, thats less than half an inch.

 

[rmediver2002]

President Clinton dropped selective availability in May of 1999.

If you are interested in thanking the government, you can thank them for GPS and the satellites that support it.

 

[O2BBubbleFree]

Thank the government for the inaccuracy of GPS. The gov't uses Selective Availabilty, which is a program that makes GPS innacurate by a varying degree, but no more than 350 feet. Nowadays, though, most GPS are WAAS enabled. WAAS is a feature that cross references radio signals from permanent land-based locations therefore making the reading accurate to .49" Yes, thats less than half an inch.

Really? Where did you find that information?

It seems to me that Garmin makes the most 'recreational' GPS units of anyone, and according to their site WAAS improves standard GPS to "better than three meters, 95% of the time."

http://www.garmin.com/aboutGPS/waas.html

I'm not an expert, but I've read about several schemes for improving position finding using GPS over the years. Generally called Differential GPS, some have used GPS + Loran, some US GPS + USSR GPS, some using RF + GPS. WAAS apparently uses the later. But I really doubt if anything gives sub-inch accuracy, especially in a unit I could afford. I know about three years ago surveyors units made by Tremble and costing thousands of $, were bragging about 1 meter accuracy.

President Clinton dropped selective availability in May of 1999.

If you are interested in thanking the government, you can thank them for GPS and the satellites that support it.

Here here! I was in volunteer alpine SAR when they dropped SA. What an improvement! What an outstanding system that the DOD has made available to the common man! Not much else I'd thank Clinton for, but that get's political

 

[Mako Mark]

Reuters headline:

"several divers were arrested and shot as spies in Saudi Arabia yesterday while the Underwater GPS unit they had been testing failed to return them to the Sinai side of the red sea.

The group had reportedly been communicating extensively before the event by internet and obviously planning for some time.

Recent connection with a similar group of underwater extreemists who trained by shooting scuba tanks in the Mojave desert is unsubstantiated, however the leader of the second group known as Kyle has dissapeared from sight."

.

 

[Fivetide]

Wonder if blue tooth would work under water? I have the tomtom software on a T740 handheld and a bluetooth connected gps.. must try that some time lol!!